1. Field of the Invention
The present invention relates to a charged particle beams exposure method and a method for producing charged particle beam exposure data for the purpose of throughput improvement when a pattern is transferred by charged particle beam exposure.
2. Description of the Related Art
Exposure of a circuit pattern of a semiconductor device using electron beam (EB) lithography technique does not require providing a mask required for exposure in photolithography, and is suitable to produce a fine pattern. However, in a variable shaping beam (VSB) scheme for dividing a pattern to be exposed into fine rectangles, thereby sequentially exposing, the number of shots is increased, and throughput is degraded. In contrast, a character projection (CP) scheme for exposing repetition patterns of some microns (characters) is introduced, thereby making it possible to restrict division into fine rectangles, and reduce the number of shots.
In exposure of a circuit pattern of a semiconductor device using an electron beam exposure apparatus as shown in FIG. 22, a pattern to be exposed is divided into fine basic patterns, and exposure of the fine patterns is repeated at the corresponding positions on a sample, thereby forming a pattern. Hereinafter, a description will be given in more detail.
An electron beam 401 emitted from an electron gun 400 is adjusted in current density by a condenser lens 402, and a first shaping aperture mask 406 is uniformly illuminated. In order to prevent irradiation into a area in which no electron beam is irradiated, a deflection voltage is applied from a blanking amplifier 403 to a blanking deflector 404, whereby the electron beam 401 is deflected, and is interrupted by a blanking aperture mask 405.
The electron beam 401 shaped in rectangle by means of the first shaping aperture mask 406 is formed as an image on a second shaping aperture mask 410 by a projecting lens 407. At this time, from a shaping deflection amplifier 408, the deflection voltage corresponding to the deflection quantity of the electron beam 401 is applied to a shaping deflector 409, whereby the electron beam is formed in a desired shape. Methods for shaping the electron beam 401 include a variable shaping beam (VSB) scheme and a character projection (CP) scheme.
In the VSB scheme, a pattern is exposed after being divided into a basic pattern of rectangle of a maximum beam size or less. The beam irradiation position is shifted relevant to a opening for VSB of the second shaping aperture mask 410, whereby a rectangular beam of its arbitrary size is shaped, and each pattern divided by using the shaped pattern is exposed.
In the CP scheme, a character of its size equal to or smaller than the maximum beam size is extracted from the pattern, and a character shaped opening is located at the second shaping aperture mask 410. A plurality of characters can be used, a beam is deflected and irradiated to a desired opening of the character shaped openings located in plurality, wherein character shaped basic patterns are exposed in all.
The shaped electron beam 401 is reduced by a reduction lens 411, and is formed as an image on a sample 417 by using an objective lens 414. At this time, the electron beam 401 is deflected by means of a main-deflector 416 to which a deflection voltage is applied from a main-deflection amplifier 415 and a sub-deflector 413 to which a deflection voltage is applied from a sub-deflection amplifier 412, whereby the deflected beam is irradiated to a desired position of the sample 417.
This procedure is repeated until all the divided patterns have been exposed. This single electron beam exposure is referred to as a “shot”. In order to carry out an electron beam shot, as described previously, at least four deflectors 404, 409, 413, and 416 are used, and voltages to be applied to these deflectors each must be changed in response to each shot.
FIG. 23 shows a relationship between a distance when a voltage is applied to a shaping deflector to move the irradiation position of the electron beam on the second shaping aperture mask and a time for its deflection voltage to be stabilized. In the case where the electron beam is significantly deflected, the corresponding large voltage is applied to the deflector. If the large voltage is applied, when the same deflection amplifier is used, a time for a voltage value to be stabilized is extended. In FIG. 23, the deflection voltage is obtained as a relationship of V1=2V2, and a time for these voltages to be stabilized is obtained as a relationship of t1=2t2.
That is, when the deflection quantity of electron beam increases, a large voltage is applied to the deflector, and a waiting time for the beam to be stabilized is extended as well. This waiting time is referred to as a “stabilization time”.
In the current electron beam exposure apparatus, the stabilization time when the maximum voltage is applied to the deflector is defined as a reference, and a stabilization time is made identical to another irrespective of the deflection voltage value.
From among these deflectors, a description will be given with respect to a main-deflector and a sub-deflector. FIG. 24A to FIG. 24C each show an exposure method using these deflectors. The sample 417 is placed on a stage (not shown), and an electron beam is irradiated while the stage moves continuously or stepwise. A unit in which this sample 417 is moved by the stage is referred to as a “frame”. As shown in FIG. 24A, a frame 500 is set in a piece shape relevant to the sample 417. That is, the sample 417 is exposed while it is moved by the stage for each frame 500.
Each frame is further exposed in each main field area 501, as shown in FIG. 24B. The main field area 501 is generally as large as some hundreds of microns to several millimeters. In the case where the stage moves stepwise, it often moves for such each main field area 501. Further, the main field area 501 is exposed for each sub field area 502. After the pattern in the sub field area 502 has been exposed, the deflection voltage is applied to the main-deflector. Then, the electron beam is deflected, and a sub field area 502 in which next exposure is carried out is selected. The size of the sub field area 502 is generally within the range from some tens of microns to some hundreds of microns, and a stabilization time of the deflection voltage to be applied from the main-deflection amplifier is often set to 1 second to several micro second.
Then, the electron beam is deflected by the sub-deflector, whereby, as shown in FIG. 24C, the shaped electron beams are sequentially shot at predetermined positions in the sub field area 502, and an EB shot pattern 503 is exposed. In general, the maximum size of electron beam is within the range from one to several microns, and the stabilization time for the deflection voltage to be applied from the sub-deflection amplifier is set to some hundreds of nanoseconds.
In the case where a character opening is selected for each EB shot, it is required to move a long deflection distance for each EB shot. A area in which a character can be selected by beam deflection using a shaping deflector of the second shaping aperture mask is within the range of some hundreds of microns to several millimeters. Therefore, the stabilization time of the deflection voltage to be applied from the shaping deflection amplifier when deflection should be carried out at the same time is extended as compared with the stabilization time of the deflection voltage to be applied from the sub-deflection amplifier required for emitting the electron beam onto a wafer for each EB shot. As a result, the long stabilization time is integrated for each EB shot, a total of stabilization times is extended, and then, exposure throughput is degraded. Even when the number of EB shots is reduced in accordance with the CP scheme, if the stabilization time is very long, exposure in accordance with the VSB scheme can improve throughput more significantly.
As described above, even when the number of EB shots is reduced in accordance with the CP scheme, if the deflection distance on the CP aperture mask is long, and the stabilization time is very long, there has been a problem that exposure in the VSB scheme can improve throughput more significantly.